IPL burn on arms
This is definitely a result of overtreatment. Fortunately your burn looks superficial and should resolve on its own in time. Make sure it keep it out of the sun as burning it can make it permanent. Many technicians who are not experienced enough do not understand that you have to turn down energies on IPL a great deal when doing off the face treatments. Please make sure you are seeing an experienced office with a physician on site. "This answer has been solicited without seeing this patient and cannot be held as true medical advice, but only opinion. Seek in-person treatment with a trained medical professional for appropriate care."
"Burn" marks from IPL are not uncommon. They usually result from treating skin that is too tan, or recently exposed to the sun. The "burn" mark is sometimes called waffling, because of the uneven appearance. It will absolutely resolve on its own, without further treatment. It is rare for it to scar, unless it is very severe. Sometimes a second low level IPL treatment will help even it out and resolve it faster. Sun protection is extremely important during the healing process.
Burns from IPL
We can understand your concerns. It does look like you were burned and it is not normal. You should make an appointment to with the supervising physician at your provider for a treatment plan to mitigate your injury.